GPS-Aided All-Accelerometer Inertial Navigation

Alan H. Zorn

Abstract:	Much research has been conducted in recent decades on developing a practical all-accelerometer inertial navigation system and on developing a practical moving- base gravity gradiometer. The former strives to measure kinematic motion in the presence of unwanted variations in gravity; the latter endeavors to measure variations in gravity in the presence of unwanted motion. Thus, goes the adage, one person’s noise is another person’s signal. In a previous paper by the author, a mathematical relationship was derived that unifies the two concepts. It was demonstrated therein that a complete solution to navigation and gravity gradient determination can be performed simultaneously, unambiguously and in real time using all-accelerometer inertial measurements only. Also, it was found that accelerometer technology is not yet of sufficient maturity to allow a practical implementation of this concept. It was noted however that advances are being made that could result in practical implementations perhaps in a decade. Certainly accelerometer-based approaches to moving-based gravity gradient determination have already been successfully implemented, but unifying gravity gradient determination with real-time navigation remains a formidable challenge. In this paper, we address a possible means of mitigating the difficulty of implementing a “pure inertial” all- accelerometer system by exploring the value of aiding the solution using GPS position fixes by means of a “loosely- coupled” Kalman filter. Simulation results projecting attainable accuracies are provided for the navigation portion of the problem, but not for expectations related to gravity gradient determination. The navigation accuracy of an airborne system is evaluated where the aircraft executes a simple constant-rate turn at constant speed and altitude. The results are compared with that of a conventional strapdown approach implemented with tactical-grade gyros and accelerometers. The simulation results suggest that accelerometer accuracies of nano-g and better are required to implement the all-accelerometer approach, even when aided using GPS. Thus realization of an all-accelerometer system using today’s sensor technologies is not feasible. Nonetheless, the approach and results contained herein should find application in determining sensor-level requirements as accelerometers of sufficient promise emerge with advancing technology. Also, a reference which quantifies the extreme accelerometer accuracy required was not found in the open literature, and this paper offers a quantification of the severity of such a challenge.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	1442 - 1453
Cite this article:	Zorn, Alan H., "GPS-Aided All-Accelerometer Inertial Navigation," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 1442-1453.
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